Can the name field of the WindowManager´s "invoke_search_popup" method be reset?
This got changed on Blender 2.79 due to a bug report I sent.
The popup menu doesn't show the last search anymore. It gets emptied, showing all the list again.
It would be cool though, if the scripter could be able to choose if he/she wants to clear the field or not, but maybe it will be necessary to file a feature request for that.